Gestational Sac: Causes and Effects

When suspecting a pregnancy, it is advisable to carry out tests to determine if you are pregnant or not. It is for this reason that home or pharmaceutical pregnancy tests have become indispensable and are taken as the first option.

When confirming a pregnancy through this method, it is advisable to measure the blood levels of the hormone human chorionic gonadotropin (HCG), thereby confirming the presence of a pregnancy.

In general, once the pregnancy is discovered, the woman must contact a specialist doctor, to carry out the corresponding studies that can determine the presence of the gestational sac, in what conditions are all its structures, so it is of choice an ecosonogram or ultrasound.

The ultrasound will define whether or not there is the presence of a gestational sac , which is nothing more than a bag that is formed so that the baby is formed inside, it contains everything necessary to preserve the life of the baby in formation.

In this bag the amniotic fluid is formed, it is observed in the ultrasound as a white border, whose center is clear.

For the formation of this should take about five to seven weeks , counted after the last menstruation, usually a transvaginal ultrasound is used to observe it.

The choice of a transvaginal ultrasound for the first months of pregnancy is due to the fact that it has greater sensitivity, which is why it will produce better and therefore clearer images. For the gestational sac to be observed, human chorionic gonadotropin levels must be between 1500 to 2000.

Look here First weeks of pregnancy: from 1st to 3rd; Complete Gestation step by step

What is the gestational sac?

It is a structure that contains the fluid in which the embryo is located, its function is to supply the necessary nutrients for it to develop in its first days of life. This will later become the placenta. But at first it is an indicator of the presence of a pregnancy, since it is the first structure that is formed and it is the one that welcomes and protects the embryo during the first weeks of life.

Normal characteristics of a gestational sac

It will only appear in the uterus when an embryo is in formation . Therefore it is a key indicator in determining a pregnancy until an embryo can be seen.

In medical terms, the uterine sac observed through ultrasound is said to be an anechoic space surrounded by a spherical hyperchoic rim and is normally located in the upper part of the uterine fundus.

Gestational age can be determined through the measurement of the sac, having an estimate of five to six weeks with a precision of more or less five days approximately.

Inside the gestational sac, a structure is formed called the yolk sac and this occurs when it reaches around 20 mm, which must contain a visible fetal pole when it reaches 25 mm.

What is an irregular gestational sac like?

It is indicative of a high risk of miscarriage. It is determined by uneven or asymmetrical edges. Its shape is important since it is the first determinant that allows evaluating the ovular vitality of pregnancy in the first weeks of life.

We recommend you read this related topic Spontaneous Abortions: Causes, Symptoms, Types and Possible Treatments

One of the forms that it can adopt is irregular and elongated, in these cases the implantation is generally low, which is called hyperotopic, where there is no evidence of a double decidual sac, so there is a high risk of abortion.

However, there is an even more serious condition, which is when the presence of a subchorionic hematoma is verified, which when it has a growth greater than 50% there is a 95% risk of abortion.

There are particularities that may occur and it is important to highlight is that if there is no embryo in the gestational sac greater than 20 mm, observed with a transvaginal ultrasound, it may be an anembryonic pregnancy, that is, without the presence of an embryo .

Determining the viability of the embryo requires the study of various ultrasonographic parameters, as well as blood tests and clinical tests. So it is essential to go to the gynecologist for a good evaluation and guidance.

Evolution per week, how does it change?

The changes occur with the passing of days, the first thing that occurs in the first 5 weeks of gestation is the evidence that there is a gestational sac.

The appearance it takes is that of a small cystic fluid collection within the unequal. The study of the signs of pregnancy according to what is observed in a transabdominal ultrasound has determined that there are two structures in early pregnancy, the double sac sign and the intradecidual sign, a condition that changes with the arrival of transvaginal ultrasounds in which these signs were determined to be 35% absent in the gestational sacs.

It is for this reason that a woman with a positive pregnancy test and the presence of an intrauterine gestational sac observed with a transvaginal ultrasound is indicative of the presence of a pregnancy, so the risk of finding a pseudogestational sac or a disidual cyst indicative of a ectopic pregnancy is much less.

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Inside this bag there is a 3-5 mm diameter structure called the yolk sac , for this reason the gestational age of five and a half weeks can be determined.

In week 6, the presence of the embryo is observed within the yolk sac, where there is already the presence of the heartbeat and the blinking movements of the embryo are observed.

Gestational sac inside the uterus

The gestational sac must be inside the uterus under normal conditions, which will indicate that it is not an ectopic pregnancy. So the presence of it inside the uterus is a sign of viability for the formation of an embryo. This condition is observed in a clearer and more precise way with a transvaginal ultrasound, where its shape and location will be determined as well as various parameters to evaluate its condition.

The time when the possibility of observing this structure inside the uterus is presented is approximately after two weeks after ovulation or four to five weeks after the first day of the last period seen. The sac can be seen attached to the endometrium, in normal gestation conditions . And it is visualized as a fine hypoechoic line around a hyperechoic line.

What is a gestational sac outside the uterus like?

It will be determined by the presence of it in places such as the fallopian tubes, a condition that occurs after ovulation. It is a condition not suitable for life, since the only structure that contains the conditions or viability for an embryo is the uterus.

An ectopic pregnancy can generate a pseudo sac, its shape is regularly irregular and it does not have a hyperechoic ring and inside it contains fluid or blood, which on ultrasound a black cavity is observed.

Find out more about this topic  Ectopic Pregnancy: Signs, Treatments, Risks and Symptoms

The difference of both gestational sacs is the amount of blood supply they have , in the normal one within the uterus, it has an intense vascularization around it, on the other hand, the pseudo gestational sac blood supply is not as abundant and does not follow the same pattern.

Ectopic gestation is a complication that occurs at the time of descent of the embryo through the tube, the implantation does not reach the uterus, but remains outside it in a place not suitable for its development.

This condition in women is a frequent cause of death (1.8 out of every 1000 pregnancies), a situation that occurs in the first three months of pregnancy. Therefore, absolute care and exhaustive medical evaluation with the corresponding ultrasounds and blood tests are essential to determine in time any finding that puts the mother’s life at risk.

Could the gestational sac be empty? Why?

Anembryonic pregnancy occurs when there is an absence of an embryo inside . There are several causes that can affect the process of formation of an embryo, so there is no single reason for getting this type of condition in pregnancy.

It is called by experts as a hollow egg , or they also call it a pregnancy with an empty egg, or an empty gestational sac.

It is a condition that cannot be predicted or avoided , what can be said is that there is no approved probability that it is a repetitive condition in successive pregnancies.

Therefore, situations may arise in which the mother is not aware of presenting this condition until after three months of gestation where the embryonic formation should be differentiated or visualized and give noticeable signs of life.

It is a condition that occurs due to a failure in any of the cell division processes at the time of conception, because from the moment the ovum and sperm join (formation of 46 chromosomes), their division begins and multiplication.

Read the article we have on  Ovulation Symptoms: Calendar, Symptoms, How to detect it and Types

The division of these chromosomes results in the duplication of the genetic material, which must be exact in both parts, any mistake or accident during this division leads to serious consequences. So it is a process that must occur perfectly.

In the process of cell division, one part is used for the formation of the gestational sac and the other for the formation of the embryo. In cases where an empty sac is produced, it is a consequence of this stage of cell division, since the cells that are designed and destined to form it follow their perfect course and give rise to such a structure, the opposite happening to cells. that divide to form the embryo, the process being paralyzed and therefore its absence within the sac, which is why the so-called hollow egg is produced.

Why is it called an anembryonic gestational sac?

It is due to the absence of an embryo within this structure.

The cause of the absence of embryo within the gestational sac is imprecise, because it is a process that occurs during the first divisions, where cells specialize due to their genetic load to the formation of the gestational sac and the embryo, in In this process, the cells that form it continue their function and generate said structure, but the cells destined to the formation of the embryo stop their division and therefore do not generate the embryo.

Pregnancy continues its normal course, with the corresponding hormonal loads, without signs of any abnormality, so that the woman generally does not present any apparent signs that indicate that this condition is present.

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The only way to diagnose an empty gestational sac is through an ultrasound and the time in which this condition can be determined is from week 7 or 8 of gestation.

The procedure that should be carried out in such a situation is to perform a uterine curettage on the woman or better known as curettage. There are situations in which it is possible to wait for the expulsion of the uterine sac to occur naturally and spontaneously, so each case in particular must be evaluated very well.

In studies carried out, it has been determined that 15% of pregnant women have the possibility of presenting an empty gestational sac and being candidates for a curettage or spontaneous abortion.

There is doubt as to how long the woman should last to try a pregnancy again and also the uncertainty that a similar case will occur again, a situation that can psychologically affect the woman.

Due to this, the necessary guidance from a good specialist should be received to try to clarify any doubts regarding the episode that occurred.

The woman can try a pregnancy again once she has recovered from the uterine curettage and is in her fertile period , the fact of having presented an anembryonic pregnancy does not mean that it can occur again in subsequent pregnancies, so a good orientation to the A woman can offer you confidence and emotional stability in the process of a new pregnancy.

No matter how the pregnancy symptoms occur as a result of the hormonal discharges that occur and the gestational sac is formed, an empty or anembryonic sac cannot be classified as pregnancy, because a pregnancy is determined by the formation of an embryo.

Don’t forget to also read  5 Weeks of Pregnancy; Complete Gestation step by step

When does the gestational sac appear?

As a general rule, it can be visualized through a transvaginal ultrasound from the fourth or fifth week of gestation, at this time the structure only reaches approximately 3 to 4 mm.

What is a fundic gestational sac like?

It means that it is at the bottom of the matrix. In the womb there is the front part that is the front part of the womb with respect to the mother and the back part that is closest to the mother’s back. Therefore the placenta can be inserted both in the anterior wall and in the posterior part and both cases are considered normal.

What is a hypotonic gestational sac like?

The hypotonic sac indicates decreased mobility or tone.  It can be the product of many causes, including the intake of medications such as Prednisolone during pregnancy, which among its side effects are loss of tone, miscarriages and premature births and palatal malformations.

This condition can be diagnosed with a study with an ultrasound, which will detect that the tone of the gestational sac will not be within normal parameters, a follow-up and comparison of the results will be carried out, and this is where a correct diagnosis can be obtained. and the care and pertinent actions for this case.

The woman who is taking treatments with Prednisolone during pregnancy should take special care and vigilance and adjust their doses to ensure the least possible damage to the baby, especially to closely evaluate and assess the function of the baby’s adrenal glands at the time of birth.

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Gestational sac and yolk sac

The differences between the two are very marked both in function and structure, but even so, those who are not familiar with medical terminology can confuse both terms and misuse them.

The yolk sac is a dark circular shaped structure found within the gestational sac. Its visualization is spent 5 weeks through a transvaginal ultrasound.

The yolk sac works by fulfilling the circulatory function of the embryo in the first weeks of life, giving rise to the first blood vessels providing the nutrients that the embryo needs for its proper development.

Then this membrane changes its structure and decreases as the embryo grows competing for space, it is not really known how long the yolk sac remains active, over time it is incorporated into the primitive intestine of the embryo.

The gestational sac is the structure that is around the yolk sac , with development of the embryo and the needs that the yolk sac can no longer meet, the gestational sac becomes a placenta and connects the blood circulation of the mother and the fetus for its nutrition and oxygen supply.

In short, there are two structures that give the embryo protection, nutrition and oxygen (among other substances) for its survival, but each with its time and defined period of each stage of the embryo’s development.

Low implantation gestational sac

It carries risks, it indicates that the placenta was implanted in a very low place that with the growth of the baby could be affected by the pressure that it exerts and produce bleeding and risk of abortion.

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The low placenta is called placenta previa and the consequence of which can lead to occlusion of the cervix, which causes bleeding before delivery, it can also interfere with delivery due to obstruction of the cervix.

Can the gestational sac have fluid?

It has amniotic fluid , but when there is an excess of it, it is called polyhydramics. Condition that can occur in the second trimester of pregnancy and can lead to serious complications for the baby and the mother respectively.

One of the functions of amniotic fluid is to protect the fetus by giving it enough space for it to move and to develop within the uterine cavity without problems.

When polyhydramnios occurs, it is the consequence of a congenital defect of the baby’s digestive system, which does not allow him to regulate the amount of amniotic fluid with his swallowing.

One in every 200 pregnancies has this pathology, which apart from being the product of a deficit in the functioning of the baby’s digestive system, is also often complicated by brain or nervous system problems.

Studies carried out by the specialist Vespucio Ricardo Díaz Serani, showed that there are excess fluids that are slight and are not associated with pathological problems in the baby, so he describes three factors that could respond to these things, such as:


  1. Gestational diabetes.
  2. RH incompatibility.


  1. Multiple pregnancies
  2. Infections that affect the fetus.
  3. Genetics.
  4. Problems in the digestive and nervous tract of the fetus.
  5. Fetal anemia
  6. Heart failure


The placenta can affect in these cases when placental tumors occur, which prevents the fetus from receiving the necessary nutrients for its formation and leads to some of the causes described above in the fetus, which can induce an increase in amniotic fluid.

What does beta HCG negative gestational sac mean?

Beta HCG is a fairly reliable indicator of pregnancy , many women in their desire to get pregnant are psychologically affected, causing changes in their body and generating the symptoms of pregnancy. So they undergo tests like beta HCG.

We recommend reading the following for more information  What is HCG Hormone and its weekly table of values

False negatives and false positives

This test, under the conditions described above, can give false positives or, if not, they can present false negatives, so it can be said that it is not infallible.

When the ovum is fertilized, hormonal changes begin in the mother in a progressive way, reaching their maximum levels when the embryo has already implanted. One of the hormones that act during this process is beta HCG, so an early test to detect its presence in the blood can give false results.

In patients who are subjected to treatments for fertilization, the beta HCG figures can be affected , which can give erroneous results.

Gestational sac with detachment, what happens?

It can be due to various causes, including a hematoma, everything will depend on the stage of pregnancy in which it is found, since a placental abruption in the first trimester can lead to a slight fetal risk, but a placental abruption in the last three months of pregnancy can lead to serious consequences.

Among the problems that can occur are very important bleeding , which can be followed by symptoms such as a very hard belly to the touch, abdominal pain, light bleeding, so you should see a doctor immediately.

This pathological condition of pregnancy usually occurs in 20% of cases . It can be diagnosed with an ultrasound, acting early can make a difference and save the lives of both mother and baby.

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During the first months this condition is called trophoblast detachment, after this time it is called placental detachment.

What is called a non-evolutionary gestational sac?

It means that the fetus is found but no heartbeat or heart activity is heard . Situation that leads to an early interruption of pregnancy, turning into a spontaneous abortion.

Among the influencing causes we have the following:

  • Health problems in women such as: inflammation or pelvic infections.
  • Poor implantation of the fertilized egg in the uterus, or implantation of the same outside the uterus.
  • Gestational sac detachment, due to lack of adherence or detachment.
  • Anembryonic gestational sac.
  • Failures in the development of the embryo.
  • Genetic or chromosome malformations incompatible with life.
  • Use of drugs not allowed during pregnancy causing teratogenic effects.
  • Genetic mutations.
  • Advanced maternal age.
  • Advanced paternal age and the effect of external toxic substances (alcohol, cigarettes or radiation).
  • Maternal nutritional deficit.
  • Teratogenic effect of some infections such as rubella, syphilis, etc.

What is an orthotopic gestational sac?

It is a sac with habitual implantation where it must be implanted , that is, in the fundus of the uterus. In other words, it is a normal implantation of the gestational sac.

Gestational sac surrounded by trophoblastic reaction

It is a gestational trophoblastic disease, better known as hydatidiform mole, which means a bad formation of the placental tissue or trophoblast .

It is distinguished by the different degrees of damage to the trophoblast or placenta in partial mole, complete mole, invasive mole, and carcinoma. Which is nothing more than the transformation of placental tissue into another tissue, which gives formation to vesicles and cysts whose advanced stages resemble bunches of grapes.

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Kathie Sand always saw the world of beauty as the terrain on which to build her professional career, a goal that was clear to her when she was only 15 years old. Her great concern to expand knowledge led her to settle in Paris where she studied hand in hand with the best beauty professionals and with the most advanced techniques for skin care.

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